Overview of the Issue
In the early 1900s, Brazilian physician, Dr. Carlos Chagas, discovered Trypanosoma cruzi, the causative agent of the disease eventually named for him, Chagas disease. The parasite is vector-borne and widespread in Central and South America. Chagas disease remains a neglected disease afflicting mostly the poor as the vector is found in poorly constructed homes in South America. The vector, triatomine bugs, a.k.a. kissing bugs or assassin bugs, lives in the cracks and crevices of dwellings and attacks residents at night while they sleep. Recently, oral transmission of Chagas disease has also been documented. Diagnosis remains difficult as the parasite can remain in tissues for years and be largely invisible to most diagnostics.
Objectives of the Presentation
1. Describe the mechanism of transmission of Chagas disease.
2. Name the vector for Chagas disease.
3. Describe the clinical signs of Chagas disease in dogs.
4. Describe the zoonotic potential of Chagas disease for a veterinarian.
5. Describe the current status of Chagas disease in the US in humans and animals.
Key Etiologic and Pathophysiologic Points
The bite of the vector, the triatomine bug, does not transmit the parasite. The parasite is largely transmitted by exposure of the mucous membrane or the break in skin integrity with the feces of the bug! Additionally, oral transmission due to ingestion of food contaminated by vector fecal material has been repeatedly documented in South America.
Key Clinical Diagnostic Points
Reliable diagnosis of Chagas disease is problematic because of the 2 phases of the parasite in the host: acute vs. chronic/indeterminate. During the acute phase, the parasite is easily located in the peripheral blood with observation on a blood smear, PCR, or culture. However, after the initial 1–2 weeks of acute infection, the parasite moves into the tissues and becomes difficult to diagnose. Blood smears will be negative, PCR is positive in only some cases, and titers can be equivocal depending on the duration of infection. Often, tissue changes are the first time that the parasite is made apparent resulting in either heart disease or gastrointestinal pathology.
Key Therapeutic Points
No drugs are currently labeled for treatment in animals in the US, and the 2 drugs labeled for use in humans have incredible side effects. Additionally, current research indicates that long-term tissue changes are not impacted by the elimination of the parasite in dogs or humans. Luckily, the majority of human cases, 70–80%, do not develop symptoms in their lifetime.
Key Prognostic Points
Because of the lack of effective treatment in animals, euthanasia should be considered. However, if that is not an option, treatment of the ensuing dilated cardiomyopathy, megaesophagus, or megacolon is appropriate, i.e., managing the symptoms.
Summary Including 4 Key “Take Home” Points
1. Chagas disease is now a global public health issue.
2. Competent vectors exist in the majority of the southern 48 states in the US.
3. Veterinarians and veterinary staff likely have increased exposure risk to Chagas disease.
4. Vector control is the best method to prevent Chagas disease transmission to humans and animals.
References
1. Merck Veterinary Manual. https://www.merckvetmanual.com/circulatory-system/blood-parasites/trypanosomiasis.
2. https://www.frontiersin.org/articles/10.3389/fmicb.2017.00607/full.
3. Santana RG, Guerra M, Sousa DR, Couceiro K, Ortiz JV, Oliveira M, Guerra JO. Oral transmission of Trypanosoma cruzi, Brazilian Amazon. Emerging Infectious Diseases. 2019;25(1):132–135.
4. T Araujo-Jorge, J Telleria, JR Dalenz. History of the Discovery of the American Trypanosomiasis (Chagas disease).
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4900435/#bib44.
6. Curtis-Robles R, Auckland LD, Snowden KF, Hamer GL, Hamer SA. Analysis of over 1500 triatomine vectors from the southern US for Trypanosoma cruzi infection and discrete typing units. Infection, Genetics and Evolution. 2018;58:171–180.
7. Zingales BS, Miles MA, Campbell DA, Tibayrenc M, Macedo AM, Teixeira MM, Schijman AG, Llewellyn MS, Lages-Silva E, Machado CR, Andrade SG, Sturm NR. The revised T. cruzi subspecific nomenclature: rationale, epidemiological relevance and research applications. Infection, Genetics and Evolution. 2012;12(2):240–253.